A device described in Japanese Patent Application Publication No. 2008-207643 (JP 2008-207643 A) (Patent Document 1) is already known as such a control device that controls a vehicle drive device as described above. The names of members in Patent Document 1 that correspond to members in the present invention are referred to in parentheses “[ ]” in the description of this section “BACKGROUND ART.” In this control device, one of a plurality of shift engagement devices [fastening elements] included in the speed change mechanism [automatic transmission AT] is brought into a slip engaged state upon a change from EV mode to HEV mode. In this state, the disconnecting engagement device [start clutch CL1] is engaged, and the rotational speed of the rotating electrical machine [motor-generator MG] is increased to crank the internal combustion engine [engine E]. Such slip of the predetermined shift engagement device reduces start shock due to unstable torque during this period being transferred to the wheels.
As also recognized in Patent Document 1, a target shift speed in the speed change mechanism is sometimes changed in the mode switching operation involving starting of the internal combustion engine. For example, in the case where a large driving force is required in order to drive a vehicle, starting of the internal combustion engine and downshift (change to a shift speed with a relatively high speed ratio) are sometimes requested. Taking such a case into consideration, the control device of Patent Document 1 slips the shift engagement device, which is disengaged when shifting from a shift speed that has been formed at the time the internal combustion engine start control is started to a shift speed adjoining this shift speed, as the “predetermined shift engagement device” described above. Slip control for reducing start shock and slip control for shifting is thus performed by common control. Accordingly, even if an internal combustion engine start control request and a shift request are received at the same time, each control can be smoothly executed.
An actual rotational speed of an input-side rotating member in the speed change mechanism increases with the internal combustion engine start control. This increase in actual rotational speed can be regarded as being about the same regardless of the vehicle speed or the shift speed. On the other hand, a virtual increase in synchronous rotational speed due to the change in shift speed is determined proportionally to the vehicle speed according to the speed ratio of each shift speed as well. Accordingly, depending on the vehicle speed, the rotational speed of the input-side rotating member which increases with the internal combustion engine start control exceeds a synchronous rotational speed at the changed shift speed (the degree of progress in shifting reaches 100%). As a result, the shift control is immediately terminated, and subsequently the rotational speed of the input-side rotating member decreases (see FIG. 16 of the present application), whereby comfortable traveling performance may not be ensured. It is not impossible to suppress the increase in rotational speed of the input-side rotating member by adjusting an oil pressure to be supplied to the shift engagement device to be slipped (see FIG. 17 of the present application). In this case, however, the torque that is transferred to the wheels rapidly increases accordingly, whereby comfortable traveling performance may not be ensured.